Magnetic amplifiers



Nov. 18, 1958 D. J. SIKORRA ET AL 2,861,240

MAGNETIC AMPLIFIERS Filed July 30, 1954 5 Sheets-Sheet 1 CONTROL CHANNEL X CHANNEL Y INVENTORS DANIEL J. SIKORRA JOHN A. WOLFE ATTORNEY Nov. 18, 1958 D. J. SIKORRA ET AL 2,861,240

MAGNETIC AMPLIFIERS Filed July 30, 1954 s Sheets-Sheet 2 CONTROL CHANNEL X A. 0. SOURCE CHANNEL Y 1N VENTORS DANIEL J. SIKORRA JOHN A, WOLFE 715. Z Y lay 5, 61

ATTORNEY Nov. 18, 1958 D. J. SIKQRRA ETAL 7 2,361,240

' MAGNETIC AMPLIFIERS Filed July so, 1954 s Sheets-Sheet 3 CONTROL IN VENTOR DANIEL J. SIKORRA JOHN A. WOLFE ATTORNEY amplifier the windings were substantially as shown.

United States Patent MAGNETIC AMPLIFIERS Daniel I. Sikorra, Champlin, and John A. Wolfe, St. Paul, Minn., a'ssignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application July 30, 1954, Serial No. 446,769

2 Claims. (Cl. 323-89) This application "relatest'o improvements in magnetic amplifiers and particularly in the field of self-biasing magnetic amplifiers. I

It is an object of this invention to provide a magnetic amplifier having a self-biasing arrangement to eliminate the fixed bias supply normally required. g

It is a further object of this invention to provide a method of using magnetic cores of material having a high flux density, such assilicon steel or 50% oriented nickel alloys which has excellent magneticpropertie for magnetic amplifiers, and eliminating the difficulties normally encountered with fixed bias in using such materials because of the high coercive force of high flux density materials. I

These and other objects and advantages of our invention will'be'understood uponconsideration of'the accompanying specification, claims and drawingsof which:

Figure 1 is a diagrammatic representation of a selfbiasing push-pull incomplete bridgemagnetic amplifier. I

Figure 2 is a diagrammatic representation of a selfbiasing doubler type magnetic amplifier, and

Figure 3 is a modification'of Figure 1.

Referring now to Figure 1, there is shown four saturable reactors A, B, C and D, the cores being preferably of-silicon steel or 50% oriented nickel alloy which have a hi'gh maximum flux density and a high coercive force. Reactors A and B and the associated windings constitute a first magnetic amplifier, of 'the incomplete bridge type, which will be referred to as channel X. Reactors C and D constitute a second magnetic amplifier, channel Y, and

the two channels constitute a self-biasing push-pull mag- 'netic amplifier stage having a differential D. C. output. The reactor windings numbered 1 2 on each core are th'e'reactance or powerwindings. Thewindings 34 in each reactor are the control or-input windings, and windings numbered 5'-6 are harmonic windings. The windingsnumbered 7-8 and910 on each reactor are-first and second bias windings respectively. The odd numbers represent'the beginnin'g'of the winding and the even numbers re'presentthe end of the winding.

The reactors are not limited to this number of windings, as for example there may be two control windings *oneach reactor energized from separate signal sources if desired, however, in one successful embodiment of the The cores have been shown as two legged cores for convenience, however, they may be of any suitable type.

The amplifier is energized from'a source of A. C. potential connected to terminals 10'and 11. A conductor 12 connects terminal '11 to a'terminal '13 of an incomplete bridge, which includes in one leg a rectifier 14 in series with reactance winding A1-2 which connectsto a second terminal 15 of the bridge. A second leg of the bridge connected to terminal 13 includes rectifier 16 in series with reactance winding B21'which connects to a third terminal=17 on the bridge. The "second terminal 15 and third terminal 17 are connected to the'incomplete bridge fourth terminal 20 throu-ghrectifiers 21 and 22 respectively. Terminals 13 and '20, ar -rhea. '0. terminals at the bridge and terminal 2911s connected back to source terminal 10by c'onduc'tors23 and 24. Terminals 15. and

17 are the D. C. terminals of "the bridge and are connected by a circuit which extends from terminal '15, through a conductor 25, a winding 26 on a load device 27, such as a diiierentialsolenoid, througha conduct or301to bias winding B8-7, to bias winding A8-7, to bias winding D10 9, to bias winding.'C10 9 and through a conductor 40 is connected back to source 10 lbyjcondu'ctors '43 and 24. Terminals 35 and 37 are theDJC. terminals of the bridge andare'connected by'acircuit which extends from terminal 35 through "a conductor 45, a second winding 46 on the load device '27, through 'a conductor "50 to bias winding D8-7, to bias 'Wi'ndin'gfCSJ, to bias Winding 310-9; to bias winding A10 9 and through a conductor '51 to the other DJC. terminal 37 0f the bridge. -A D. C. inpu't current of reversible polarity is connected to input'ter'minals 52 and 53. The control windings are connected in a seriescircuit which includes-"a conduct0r 5 4-connectin g the terminal 52 to poiitiol I wind- "ing A3'-'4,-control winding B3 4, c0n'trol winding C'43,

control windingD4-3, an'd a'conduc'tor 55 back to'the other input terminal 53.

The harmonic "windings AS- 6, B5 6, C5-6 and D545 are connected in series and the circuit is closed byfa capacitor 56 making a low impedance loop for 'the harmonic frequencies.

, Referring now to Figure 2, there is shown a modificationof "Figure l in whicha pair of magnetic amplifier doubler circuits are connected in push-pull in the selfbiasing arrangement of the invention and .provide an A. C. output of reversible phase. Four saturable reactors E, F,'G and'H each have a power winding 1+2, a control winding 3 1, a harm'onic winding 5 6, and first. and

second biasing windings 7-8 and 9-10 respectively.

Reactors E and F with their associated circuit constitute a first self-biasing magnetic amplifier doubler stage and reactors G and H constitute a second similar doubler stage. The two doubler stages are connected inparallel and form a push-pull amplifier which provides an A. ,0.

output. The amplifier receives its energization froma "source of A. C. potential which is connected to terminals 10 and 1 1. A conductor 70 connects terminal 11, to

reaetance'windin'g E2-1 which has inseries withit bias windings F7-'8-aindH9-j10, a rectifier 71 and the upper portion of a primarywinding 7 2 of an output transformer 73. A center tap 74; of primary winding .72 is connected to the A. C.-termi nal10 by'a conductor 75.- A conductor 76 and part'of conductorjtl connect the, A. C. terminal *11'to reactance winding Fl-2 which has in series with. it bias windings G10 9 and E3 7, a rectifier 77 and the upper portion of primary winding 72 of transformer '73. Thus reactance winding E1-2 and reactance winding "F1'2 and 'theii 'ass'ociated circuit elements including rec tifiers 71 and 77 respectively are connected in parallel but with the polarity of the 'rectifiers reversed'so that the windings conduct on alternate half cycles.

Looking now at the lower doubler circuit a conductor 80 con'nec'ts'the A. Cite'r'minal -11 to reactance winding G2-1 which has connected in series therewith bias wind- .backto A. C. terminal through conductor 75. A conductor 82 connects terminal 11 to reactance winding H1-2. The other end of the reactance winding is connected in series with bias winding G8-7, bias winding E10-9, a rectifier 83, through the lower portion of trans former winding 72, and back to A. C. terminal 10 through conductor 75. Reactors G and H are thus connected in parallel but are polarized by the rectifiers 81 and 83 res ectively so that they conduct current on alternate half cvcles. The control windings and harmonic windings of Figure 2 may be the same as described for Figure 1.

Referring now to Figure 3 there is shown a modification of the self-biasing circuit of Figure l, in which the basic difference is that each reactor has one bias winding thereon. The reactance windings of the reactors are energized from a center tapped secondary winding of a transformer 90. The primary winding of the transformer is connected to A. C. source terminals 10 and 11. The upper terminal 91 of the secondary winding is connected through a conductor 94 and a rectifier 95 to reactance winding A1-2, and through a conductor 96 and a rec ifier 97 to reactance winding C1-2. The lower terminal 92 of the secondary winding is connected throu h a conductor 99 and a rectifier 100 to reactance winding D1-2,

and through a rectifier 98 to reactance winding B1-2. The reactance windings A1-2 and 31-2 have their terminals 2 connected to winding 26 of load device 27, previouslv mentioned. Reactance windings C1-2 and D1-2 have their terminals 2 connected to winding 46 of load device 27. The other terminals of the windin s 26 and 46 are formed at a junction 101. Junction 101 is connected through a conductor 102 to series connected bias windings D8-7, C8-7, B8-7 and A8-7. Terminal 7 of bias winding A8-7 is connected by a conductor 103 to the center tap connection 93 of the secondary winding of transformer 90. The control and harmonic windings of this figure are connected in the manner explained in Figure 1.

Operation In Figure l the self-biasing incom lete bridge magnetic amplifier operates substantially as follows. Each of the reactor cores A, B, C and D has wound thereon a reactance winding and each reactance winding has a rectifier, such as a selenium rectifier, in series with it so that current will flow in only one direction through the reactance winding to obtain a self-saturating circuit, as is well known in the art. These rectifiers are connected so that the two reactance windings of reactors A and B conduct on alternate half cycles. Likewise the rectifiers 41 and 42 associated with the reactance windings of reactors C and D are connected so that the reactors C and D conduct on alternate half cycles of the supply current. Reactors A and C conduct together on one half cycle and reactors B and D conduct on the opposite half cycle. For purpose of explanation let us assume the instantaneous polarity when terminal 11 is positive so that the reactance windings of reactors A and C are conducting. The load current flows from terminal 11 through conductor 12, rectifier 14, reactance winding A1-2, junction 15, conductor 25, winding 26 of a differential solenoid 27 or other suitable load device, conductor 30, through biasing windings B87, A8-7, D10-9, and C10-9 which are connected in series, through conductor 31, junction 17, rectifier 22, and conductors 23 and 24 back to terminal 10. Likewise current flows from terminal 11 through conductor 32, rectifier 34, reactance winding C1-2, junction 35, conductor 45, winding 46 of load 27, conductor 50 to bias windings D8-7, C8-7, B10-9, and A10-9 which are connected in series, through conductor 51 to junction 37, rectifier 42, conductors 43 and 24 back to terminal 10. When no control signal is present reactors A and C conduct equally so that equal and opposite currents flow in the differential windings of the load device 27 resulting in zero output. The load current of reactor A flows through a bias winding of each of the four reactors and in each case the flux set up in the core by the biasing winding current is in opposition to the flux established by the reactance winding of each core. Likewise, the load current of reactor C fiows through a second bias winding of each reactor, the flux set up by these biasing windings being magnetically additive to that produced by the other biasing windings and opposing the flux produced by each of the reactance windings. Since the reactance windings of reactors A and C are now conducting the biasing windings on these reactors have little if any effect during this half cycle due to the fact that there are very few turns on the bias winding compared to the reactance winding, however, in reactors B and D where the reactance windings are not conducting the bias Windings are presetting the cores for the succeeding half cycle. As was, previously stated, in the absence of a control signal the reactors conduct equally so that the two bias currents in each reactor are substantially equal and additive.

The amplifiers are biased class A and the control windings which are connected in series are connected so that a signal of a given polarity which would tend to decrease the output of reactors A and B tends at the same time to increase the output of reactors C and D by an equal amount. Thus the circuit of Figure 1 is truly a pushpull stage. Let us now assume a control signal is applied to the amplifier of the polarity indicated on the drawing such that terminal 52 is positive. The signal is such as to reduce the output of reactor A and increase the output of reactor C by an equal amount. It should be clearly seen that the summation of the bias currents on each reactor remains substantially constant regardless of the signal applied since the current in one bias winding is increased as the current of the other bias winding is decreased.

In the same manner of operation as previously de scribed, when the instantaneous polarity of the source has reversed so that terminal 10 is positive with respect to terminal 11, the reactance windings of reactors B and D will conduct. The same bias windings which were in series with windings A1-2 and Cl-2 are also in series with windings B1-2 and D1-2 respectively and the load current of these reactors flows through the bias windings as previously explained, now presetting the cores A and C for the subsequent half cycle.

Biasing the amplifier with its own output in the manner described above does not produce feedback as one might assume. If in response to a change in control current channel Y increases its output by AI and channel X decreases its output by AI there will be a negative feedback efiect of N AL and a positive feedback elfect of N AI on each core, where N is the number of turns on the bias winding. If AI equals A1 the net feedback will be zero.

Referring now to the self-biasing push-pull doubler circuit of Figure 2 the operation can be described as follows. Each of the reactors E, F, G and H has wound thereon a reactance winding. A rectifier is connected in series with each reactance winding to permit current to flow therethrough in one direction. The rectifiers 71 and 77 are polarized so that the reactance windings of reactors E and F, which constitute channel X, conduct on alternate half cycles. The rectifiers 81 and 83 are polarized so that the reactance windings of reactors G and H which constitute channel Y, conduct on alternate half cycles. Reactors E and G conduct together on one half cycle and reactors F and H conduct together on the succeeding half cycle. Let us assume an instantaneous polarity such that terminal 11 is positive with respect to terminal 10. Current then flows from terminal 11 through a series circuit whichincludes conductors 70. and 76, reactance winding F1-2, bias windings G-9 and"E8 .,7, rectifier 77, the upper portion of winding 72 of output transformer 73, terminal 74 and through conductor 75 back to terminal 10. Simultaneously current flows from terminal 11 in a series circuit through conductor 82, reactance winding H1-2, bias windings G8-7 and E10-9, conductor 84, rectifier 83, junction 85, the lower portion of output transformer winding 72, terminal 74 and through conductor 75 back to terminal 10. Thus during the half cycle when reactors F and H are conducting the load current of these reactors flows through the bias windings of reactors E and G presetting the cores for their succeeding half cycle of operation. Since the amplifier is designed to operate class A and in push-pull, a control signal which increases the output of reactor F also decreases the output of reactor H by an equal amount, and vice versa. The magnetic summation of the biasing currents applied to cores E and G, therefore, is relatively constant regardless of the signal applied.

At balanced conditions, i. e. no control signal, the output currents of reactors F and H are equal so that the two currents fed to the center tapped transformer winding 72 are equal and opposite. The fluxes produced by the two currents cancel and there is no potential induced in the secondary winding 86. When a control signal is applied across terminals 52 and 53 so that, for example, the output of reactor F is decreased and the output of reactor H increased, then the opposing currents in the transformer winding 72 are no longer equal and an A. C. output potential of one phase results. If the D. C. control signal polarity is reversed an A. C. output potential of the opposite phase will be produced.

When the instantaneous polarity of the supply has reversed, so that terminal 10 is positive with respect to terminal 11, reactors E and G will be conducting in the same manner as previously described for reactors F and H, and when there is no control signal equal and oppo site currents will flow in center tapped winding 72 producing equal fluxes in the output transformer which cancel resulting in zero output. The biasing windings H10-9 and F8-7 are connected in series with reactance winding E12 and the biasing windings H8-7 and F10-9 are connected in series with reactance windings G1-2. The load current from reactors E and G flowing through these biasing windings presets the cores F and H for the succeeding operating cycle.

Referring now to Figure 3 the operation may be described as follows. Each of the reactors A, B, C and D has wound thereon a reactance winding. A rectifier is connected in series with each reactance winding to allow current flow in one direction through the windings. The reactors are energized from the secondary winding of power transformer 90. The secondary winding has a center tap 93 and a pair of terminals 91 and 92. The windings on reactors A and C are connected to terminal 91 and conduct during one half cycle, and the windings on reactors B and D are connected to the terminal 92 and conduct during the succeeding half cycle. Reactance windings A and B are connected to winding 26 of the load device27 which may be a differential solenoid. Reactance windings C and D are connected to the winding 46 of the load device 27. The other terminals of load windings 26 and 46 are connected together at a junction 101, A circuit exists between junction 101 and center tap 93 and may be followed through conductor 102, bias windings D8-7, C8-7, B8-7 and A8-7, and through conductor 103 to center tap connection 93.

The amplifier is biased class A so that with no control signal applied equal currents flow in windings A12 and Cl-2 during one half cycle and in windings B1-2 and D1-2 during the succeeding half cycle. This results in equal and opposing currents flowing in the solenoid windings so that the output is zero. The two currents are summed at junction 101 and both currents flow through the ias wimi gh urre t flowi a h oughthabias winding of each reactor is always, Substantially, constant regardless of the signal applied. When a control signal is applied to terminals 52 and 53 which tendsto reduce the current in reactor A it tends to increase, the current in reactor C by an equal amount. This results in an output at load device 27 due to unequal currents, in windings 26 and 46, however, the sum of thesecurrents re; mains substantially constant to provide a constant bias current. The operation of this circuit is verynearlythe same as for Figure 1 with the exception that the currents are summed andput through a single bias winding in Figure 3 while in Figure 1 the currents of the separate, channels are put through separate bias windings and summed magnetically.

In Figures 1, 2 and 3 each of the reactors has a wind: ing numbered 56 which is called a harmonicwinding. These windings are connected in series, as would bea conventional bias winding, and the circuit is closedby a capacitor 56. In a push-pull circuit at balance, the voltages which produce second harmonic currents tend to cancel each other out in a control winding. However, in the bias winding of a conventional push-pull, these, harmonics are free to flow since the induced second har-. monic voltages add. With self-bias it was found helpful to provide a separate path of flow for these harmonics, and thus the harmonic winding has been provided.

Many changes and modifications of this invention will undoubtedly occur to those who are skilled in the art and we therefore wish it to be understood that we intend to be limited by the scope of the appended claims and not by the specific embodiments of the invention which are disclosed herein for the purpose of illustration only.

We claim:

1. A push-pull magnetic amplifier comprising in combination: first and second magnetic amplifier channels, each of said channels including a pair of saturable reactors; a self-saturating reactance winding, a control winding, and first and second bias windings on each of said reactors; each of said self-saturating reactance windings having a rectifier in series to allow current flow in one direction through said reactance winding; a source of alternating current potential; circuit means connecting the self-saturating reactance windings of said pair of reactors from said first channel to said source in parallel; circuit means connecting the self-saturating reactance windings of said pair of reactors from said second channel to said source in parallel, the rectifiers associated with said first channel reactors being poled to allow current flow therein during one half cycle of said alternating source, the rectifiers associated with said second channel reactors being poled to allow current flow therein during the succeeding half cycle of said alternating source; a source of signal potential; circuit means connecting said signal in opposing relation, respectively, to the control windings of the reactors of said first channel; circuit means connecting said signal in opposing relation to the control windings, respectively, of the reactors of said second channel, whereby a signal applied to the reactors of said first channel tends to increase the conductivity of one reactor and simultaneously decrease by an equal amount the conductivity of the other reactor; first and. second load circuit means, said first load circuit means comprising a load impedance and said first bias windings connected in a series circuit so that current flowing through said load circuit flows through said bias windings, said second load circuit means comprising a load impedance and said second bias windings connected in a series circuit so that the current flowing through said second load circuit flows through said second bias windings; circuit means connecting said first load circuit in series with saidfirst channel reactance windings; and circuit means connecting said second load circuit in series with said second channel reactance windings.

2. A push-pull magnetic amplifier comprising in combination: first and second magnetic amplifier channels, each of said channels including a pair of saturable reactors; a reactance winding, a control winding, a harmonic winding, and first and second bias windings on each of said reactors; each of said reactance windings having a'rectifier in series to allow current flow in one direction through said reactance winding thereby providing a selfsaturating circuit; circuit means connecting the self-saturating reactance windings of said pair of reactors from said first channel in parallel; circuit means connecting the self-saturating reactance windings of said pair of reactors from said second channel in parallel; a source of alternating current potential; connection means connecting said source in energizing relation to said channels, said rectifiers in said first channel being poled so that the current flows through said first channel reactors during one half cycle of said source, said rectifiers in said second channel being poled so that current flows through said second channel reactors during the succeeding half cycle; first and second load circuit means included in said connection means, said first load circuit means comprising a load impedance and said first bias windings connected in a series circuit so that current flowing through said load circuit flows through said bias windings, said second load circuit means comprising a load impedance and said second bias windings connected in a series circuit so that the current flowing through said second load circuit flows through said second bias windings; circuit means connecting said first load circuit in series with said first channel reactance windings; circuit means connecting said second load circuit in series with said second channel reactance windings; means connecting said control windings in series and to a source of signal potential; and means interconnecting said harmonic windings in a low impedance loop.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Publication: Magnetic Amplifiers of the Balance Detector TypeTheir Basic Principles, Characteristics, and Applications, by W. A. Geyger, AIEE Miscellaneous Paper, to 93, December 1949. 

